A damper provides a damping force in reaction to motion. A damper is typically filled with a damping fluid to provide fluidic resistance to the motion of a piston traveling through the damping fluid. A conventional piston generally includes valves for compression flow of damping fluid and valves for rebound flow of damping fluid. In this regard, shims are used to block one set of valves during each motion of the piston. For example, if the damper is experiencing a compression stroke, the rebound valves are blocked by the rebound shims. Conversely, when the damper is in a rebound stroke, the compression valves are blocked by the compression shims.
Shim configuration can greatly impact the performance and damping characteristics of the damper. Generally, a combination of different thicknesses and sizes of shims (referred to as a “shim stack”) is used to tailor the characteristics of the damper during use. Shims are typically metallic discs that are capable of bending with a low rate of fatigue. In this regard, spring steel is often a material used for the shims. When the damper is in a compression stroke, and the rebound valves are blocked by the rebound shims, the compression shim stack is necessarily bent away from the compression valves to allow flow of the damping fluid through the piston. The rate of the flow determines the damping force. If the compression shim stack allows freely flowing damping fluid through the compression valves, the damping effect will be small. If the compression shim stack greatly restricts flow of damping fluid through the compression valves, the damping effect will be high.
Tuning a damper with a shim stack has an influence on the performance and damping characteristics of the damper, the shims are often configured in a manner that provides consistent and repeatable damper performance. Although the damper can be tuned within a certain range of performance by adjusting the shim stacks, the tuning capability is limited. In some cases, the damper also includes a damping fluid bypass system, often metered mechanically. The damping fluid bypass system provides pressure relief across the piston without the need for the shim stack to deflect. In this regard, a damping fluid bypass system provides an increase in the range of damping characteristics of the damper that can be tuned. Typical damping fluid bypass systems have a single mechanical metering adjustment, and do not provide a method for adjustment based on feedback by the driver and/or the road conditions.